In the late 1950s, epidemiologists believed that a fetus was a “perfect parasite” that was “afforded protection from nutritional damage that might be inflicted on the mother.” The placenta was regarded as a “perfect filter, protecting the fetus from harmful substances in the mother’s body and letting through helpful ones.” Nonchalance existed with regard to prenatal nutrition. During the 1950s and 1960s, women were strongly advised against gaining too much weight during pregnancy. During the baby boom, “pregnant women were told it was fine to light up a cigarette and knock back a few drinks.” Roughly half of U.S. mothers reported smoking in pregnancy in 1960.

But what if the nine months in utero are one of the most critical periods in a person’s life, shaping future abilities and health trajectories—and thereby the likely path of earnings? This paper reviews the growing literature on the so-called “fetal origins” hypothesis. The most famous proponent of this hypothesis is David J. Barker, a British physician and epidemiologist, who has argued that the intrauterine environment—and nutrition in particular—“programs” the fetus to have particular metabolic characteristics, which can lead to future disease."

Almond and Currie offer a thoughtful overview of the evidence that a wide array of environmental factors may have long-run effects not only on health, but also on economic outcomes like wages. These environmental factors that can affect fetal development include both extreme situations like famine, but also milder environmental factors like infectious diseases, exposure to pollution, maternal diet, and even severe weather during a pregnancy. Thinking through what constitutes cause-and-effect evidence for these issues often involves a search for a natural experiment. Two of the points they make about the implications of their argument as a whole, several points struck me with particular force:

1) There's a long-standing argument in the social sciences about nature vs. nurture, but arguments over genetic influence are getting a lot more complex these days than what I learned back in grade-school about Gregor Mendel and his pea plants. The current subject of epigenetics explores how the same genes can lead to different characteristics. As Almond and Currie write in this context about fetal effects: "[T]he hypothesized effects reflfl ect a specific biological mechanism, fetal “programming,” possibly through effects of the environment on the epigenome, which are just beginning to be understood. The epigenome can be conceived of as a series of switches that cause various parts of the genome to be expressed—or not. The period in utero may be particularly important for setting these switches."

2) While this literature is still young and growing, it could turn out to be true that one of the most important ways to help children is to help their pregnant mothers. Almond and Currie write: "[O]ne of the most radical implications of the fetal origins hypothesis may be that one can best help children (throughout their life course) by helping their mothers. That is, we should be focusing on pregnant women or perhaps even women of child-bearing age if the key period turns out to be so early in pregnancy that many women are unaware of the pregnancy. Such pre-emptive targeting would constitute a radical departure from current policies that steer nearly all healthcare resources to the sick, i.e., the “pound of cure” approach. That said, the existing evidence is not sufficient to allow us to rank the cost-effectiveness of interventions targeted at women against more traditional interventions targeted at children, adolescents, or adults."